1. Field of the Invention
The present invention relates to a thermally-assisted magnetic recording head used in thermally-assisted magnetic recording in which near-field light is irradiated to a magnetic recording medium to lower a coercivity thereof so as to record information, and a head gimbal assembly, a head arm assembly, and a magnetic disk unit which are mounted with the thermally-assisted magnetic recording head, and a light source unit used therein.
2. Description of Related Art
A magnetic disk unit in the related art is used for writing and reading magnetic information (hereinafter, simply referred to as information). The magnetic disk unit is provided with, for example, in the housing thereof, a magnetic disk in which information is stored, and a magnetic read write head which records information into the magnetic disk and reproduces information stored in the magnetic disk. The magnetic disk is supported by a rotary shaft of a spindle motor, which is fixed to the housing, and rotates around the rotary shaft. On the other hand, the magnetic read write head is formed on a side surface of a magnetic head slider provided on one end of a suspension, and the magnetic read write head includes a magnetic write element and a magnetic read element which have an air bearing surface (ABS) facing the magnetic disk. In particular, as the magnetic read element, a magneto-resistive (MR) element exhibiting magneto-resistive effect is generally used. The other end of the suspension is attached to an end of an arm which is rotatably supported by a fixed shaft installed upright in the housing.
When the magnetic disk unit is not operated, namely, when the magnetic disk does not rotate, the magnetic read write head is not located over the magnetic disk and is pulled off to the position away from the magnetic disk (unload state). When the magnetic disk unit is driven and the magnetic disk starts to rotate, the magnetic read write head is changed to a state where the magnetic read write head is located at a predetermined position over the magnetic disk together with the suspension (load state). When the rotation number of the magnetic disk reaches a predetermined number, the magnetic head slider is stabilized in a state of slightly floating over the surface of the magnetic disk due to the balance of positive pressure and negative pressure. Thus, the information is accurately recorded and reproduced.
In recent years, with a progress in higher recording density (higher capacity) of the magnetic disk, an improvement in performance of the magnetic read write head and the magnetic disk has been demanded. The magnetic disk is a discontinuous medium including collected magnetic microparticles, and each magnetic microparticle has a single-domain structure. In the magnetic disk, one recording bit is configured by a plurality of magnetic microparticles. Since the asperity of a boundary between adjacent recording bits is necessary to be small in order to increase the recording density, the magnetic microparticles need to be made small. However, if the magnetic microparticles are small in size, thermal stability of the magnetization of the magnetic microparticles is lowered with decreasing the volume of the magnetic microparticles. To solve the issue, increasing magnetic anisotropy energy of the magnetic microparticle is effective. However, increasing the magnetic anisotropy energy of the magnetic microparticle leads to increase in the coercivity of the magnetic disk. As a result, difficulty occurs in the information recording using the existing magnetic head.
As a method to solve the above-described difficulty, so-called thermally-assisted magnetic recording has been proposed. In the method, a magnetic recording medium with large coercivity is used, and when information is written, heat is applied together with the magnetic field to a portion of the magnetic recording medium where the information is recorded to increase the temperature and to lower the coercivity, thereby recording the information. Hereinafter, the magnetic head used in the thermally-assisted magnetic recording is referred to as a thermally-assisted magnetic recording head.
In the thermally-assisted magnetic recording, near-field light is generally used for applying heat to a magnetic recording medium. For example, in Japanese Unexamined Patent Application Publication No. 2001-255254 and in Japanese Patent No. 4032689, disclosed is a technology of allowing frequency of light to coincide with a resonant frequency of plasmons which are generated in a metal, by directly applying light to a plasmon generator, in order to generate near-field light. In the method of directly applying light to a plasmon generator, however, the plasmon generator itself overheats and accordingly deforms, depending on usage environment or conditions. Therefore, practical realization of the method is difficult.
As a technology capable of avoiding such overheating, in Japanese Patent No. 4104584, a thermally-assisted magnetic recording head using surface plasmon polariton coupling is proposed. In this technology, without direct irradiation of light propagating through a waveguide (guided light) to a plasmon generator, the guided light is coupled to the plasmon generator through evanescent coupling, and surface plasmon polaritons generated on a surface of the plasmon generator are used.
In the thermally-assisted recording technology, although it is important to generate fine light spots, where and how to dispose a light source (laser light) is also highly important. For example, in Japanese Unexamined Patent Application Publication Nos. 2001-143316 and 2002-298302, a configuration which includes a combination of an optical fiber and a reflective mirror and guides light to a near-field generation element is disclosed. In addition, in Japanese Unexamined Patent Application Publication No. 2006-185548, a configuration in which a unit having a heat sink and a laser diode is mounted on a back surface of a slider, and a suspension is sandwiched between the slider and the unit is disclosed. Moreover, in Japanese Unexamined Patent Application Publication No. 2008-59645, a technology in which a laser diode chip including a monolithically-integrated reflective mirror is mounted on a back surface of a slider to guide light to the slider is disclosed. Furthermore, in Japanese Unexamined Patent Application Publication No. 2006-202461, a diffraction grating which couples an electromagnetic wave in a planer waveguide is disclosed. In addition, in IEEE Trans. Magn. Vol. 42, p 2417 (2006), a light guiding method in which light emitted from a laser unit provided in a drive is irradiated to a diffraction grating is proposed. In Japanese Unexamined Patent Application Publication No. 2005-317178, an invention of forming a slider by a semiconductor laser chip (GaAs substrate) itself is disclosed. In Japanese Patent No. 3231331 and U.S. Patent Application Publication No. 2008/0002298 specification, a configuration in which a surface emitting laser is mounted on an integrated surface and light is guided to a near-field light generation element section with use of a diffraction optical element (condenser lens or grating) is proposed. In addition, the applicants have proposed a head structure in which a laser diode holder unit (LDU) supporting a laser diode chip is formed, and the LDU is mounted on a back surface of a slider (on an opposite side of an air bearing surface) provided with a read element and a write element (Japanese Unexamined Patent Application Publication No. 2008-47268).
Incidentally, in the configuration in which one end surface of the waveguide is arranged to face a light source unit such as a laser diode, there is an issue of return light, that is, part of laser light emitted from the light source unit is reflected once on a light incident surface of the waveguide, and the reflected part of the laser light enters the light emission surface of the light source unit again. In this case, to improve the optical coupling efficiency, the gap between the light emission surface of the light source unit and the light incident surface of the waveguide is desirably small as much as possible. However, when the light emission surface of the light source unit is close to the light incident surface of the waveguide, the intensity of the return light described above is increased so that stable operation of the laser diode may be obstructed.
In view of the foregoing, it is desirable to provide a thermally-assisted magnetic recording head which is excellent in recording efficiency and is operable stably.